The present invention relates to a method for removing oxygenates from an olefinic stream by converting the oxygenates in the presence of a catalyst to higher or lower boiling compounds which are more readily separable from the stream, and then removing the higher or lower boiling compounds from the stream.
Light olefins, defined herein as ethylene, propylene, butylene and mixtures thereof, serve as feeds for the production of numerous important chemicals and polymers. Typically, light olefins are produced by cracking petroleum feeds. Because of the limited supply of competitive petroleum feeds, the opportunities to produce low cost light olefins from petroleum feeds are limited. Efforts to develop light olefin production technologies based on alternative feeds have increased.
An important type of alternate feed for the production of light olefins is oxygenate, such as, for example, alcohols, particularly methanol and ethanol, dimethyl ether, methyl ethyl ether, diethyl ether, dimethyl carbonate, and methyl formate. Many of these oxygenates may be produced by fermentation, or from synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials, including coal, recycled plastics, municipal wastes, or any organic material. Because of the wide variety of sources, alcohol, alcohol derivatives, and other oxygenates have promise as an economical, non-petroleum source for light olefin production.
The catalysts used to promote the conversion of oxygenates to olefins are molecular sieve catalysts. Because ethylene and propylene are the most sought after products of such a reaction, research has focused on what catalysts are most selective to ethylene and/or propylene, and on methods for increasing the life and selectivity of the catalysts to ethylene and/or propylene.
The conversion of oxygenates to olefins generates by-products whose presence is undesirable for subsequent applications of the collected olefins. Although the separation of many oxygenates, e.g., ketones and aldehydes, from hydrocarbons such as olefins can be capably handled by existing commercial processes, the separation of other oxygenates, e.g., dimethyl ether (DME) can be problematic. DME is an oxygenate impurity formed during the conversion of methanol into light olefins which can act as a poison to downstream olefin polymerization catalysts, especially metallocene catalysts. Removal of DME from oxygenates to olefins product streams is thus highly desirable. Unfortunately, such removal can be difficult given, inter alia, DME""s physical characteristics similar to certain lower olefins, e.g., its similar volatility to propylene. Separation of DME from propylene by distillation, e.g., using a C3 splitter, requires a super fractionation column requiring significant capital investment. Alternatively, DME""s difference in solubility from lower olefins can be exploited by using a water wash to remove DME from an olefinic product stream. Unfortunately, given DME""s non-polar characteristics, an extensive volume of water would be required in a water wash tower so employed. Given these difficulties it would be desirable to provide a process for removing DME from olefin-containing streams such as those obtained by conversion of oxygenates to olefins, which does not require superfractionation or water washing.
Methods for recovering and recycling dimethyl ether (DME) from a methanol-to-chemical conversion reaction using a DME absorber tower is disclosed in U.S. Pat. No. 4,587,373 to Hsia.
Stud. Surf. Sci. Catal. (1985), 20 (Catl. Acids Bases), 391-8, discusses low temperature conversion of dimethyl ether over Pt/H-ZSM-5 in the presence of hydrogen by a bifunctional catalyzed reaction.
Stud. Surf. Sci. Catal. (1993), 77 discusses hydrogenation of oxygenates such as dimethyl ether over a Ni/Al2O3 catalyst to form methane.
U.S. Pat. No. 5,491,273 to Chang et al. discloses conversion of lower aliphatic alcohols and corresponding ethers to linear olefins over large crystal zeolites, e.g., ZSM-35 containing a hydrogenation component of Group VIA and Group VIIIA metals.
DE3210756 discloses a process for converting methanol and/or dimethyl ether feed to olefins by reacting the feed over a pentasil-type zeolite catalyst, separating C2-C4 olefins, methane and water from the reaction product and catalytically hydrogenating the remaining components over Coxe2x80x94Mo supported on alumina, optionally preceded by hydrogenation over a Gp. 8 noble metal for polyunsaturated, non-aromatic compounds.
U.S. Pat. No. 4,912,281 to Wu discloses converting methanol or methyl ether to light olefins in the presence of hydrogen and ZSM45 which is highly selective to C2-C4 olefins, especially ethylene.
DE2720749 discloses converting lower aliphatic ethers to hydrocarbons in the presence of amorphous, non-acid-activated Al silicate.
U.S. Pat. No. 4,625,050 to Current discloses the use of carbonylation to convert dimethyl ether to methyl acetate and ethanol (as well as minor amounts of methyl formate and propanol) over hydrogen and CO in the presence of heterogeneous NiMo catalyst on an alumina support.
EP-229994 discloses the removal of DME as an impurity (1-500 wppm) of olefinic hydrocarbon feedstock by passing the feedstock through an adsorbent mass of crystalline zeolite molecular sieve having the crystal structure of faujasite at 0-60xc2x0 C. and 0.15-500 psia to selectively absorb DME.
In addition to DME, light olefin products, especially those generated by steam cracking or derived from oxygenated feedstocks, can contain unsaturated by-products such as acetylene, methylacetylene (MA) and propadiene. Making olefins from oxygenated feedstocks produces a unique effluent stream that must ultimately be separated and purified to produce the high purity olefin products currently desired. These unsaturated by-products poison polyolefin catalysts, and therefore must be almost completely removed from olefin product streams. For ethylene, current manufacturing specifications can require acetylene levels to be under 0.5 mole ppm. For propylene, current manufacturing specifications can require methyl acetylene and propadiene levels to be under 2.9 mole ppm.
Catalysts for selectively hydrogenating highly unsaturated compounds are known in the art. For example, U.S. Pat. No. 6,084,140 to Kitamura et al. discloses a palladium and alumna catalyst for hydrogenating highly unsaturated hydrocarbons in olefin streams from steam cracking processes. The catalyst can hydrogenate acetylene, methyl acetylene, and propadiene, with only limited hydrogenation of the olefin products. U.S. Pat. No. 4,367,353 to Inglis discusses a hydrogenation process using a supported palladium catalyst. The process involves first fractionating the hydrocarbon streams before hydrogenating, whereby hydrogen is removed. Hydrogen is added during a subsequent hydrogenation step, allowing for greater control of the extent of hydrogenation. Because the concentration of unsaturated by-products acetylene, methyl acetylene, and propadiene can increase to three times their initial amounts during the purification of the hydrocarbons by fractionation, the concentration of acetylene, methyl acetylene and propadiene must be three times lower following front-end hydrogenation than in tail end hydrogenation. Achieving this greater purity results in greater loss of olefin products during the hydrogenation process.
U.S. Pat. No. 5,837,217 to Nielsen et al. discloses preparation of hydrogen rich gas from a feed stock of dimethyl ether and steam, wherein the dimethyl ether is reacted with steam in the presence of i) an ether hydration catalyst such as acidic zeolites, e.g. HZSM-5, and ii) a methanol decomposition catalyst, e.g., Cuxe2x80x94Zn-alumina.
Given the difficulties presented in separately removing by-products DME and the unsaturated compounds methyl acetylene, propadiene and acetylene from olefinic product streams, particularly those product streams from steam cracking and oxygenate to olefins processes, it would be advantageous to remove at least one or more of these by-products with techniques that do not require dedicated equipment for superfractionation, water washing, etc. Moreover, it would be advantageous to at least partially remove these by-products using equipment commonly found in existing olefin plant recovery trains, e.g., hydrogenation reactors. Accordingly, it would be particularly advantageous to remove DME along with the hydrocarbon impurities acetylene, methyl acetylene, and propadiene from product streams using the same equipment.
In one aspect, the present invention relates to a process for at least partially removing from a product stream comprising Cx olefin wherein x is an integer ranging from 2 to 6, an oxygenate impurity selected from dimethyl ether, diethyl ether, di-n-propyl ether, diisopropyl ether, methylethyl ether, methyl-n-propyl ether, methylisopropyl ether, ethyl-n-propyl ether, ethyl isopropyl ether, n-propylisopropyl ether, or mixtures thereof which comprises: converting said oxygenate impurity to a compound whose boiling point differs by at least about 5xc2x0 C. from said oxygenate impurity; and separating at least some of said compound from said Cx olefin.
In one embodiment of this aspect of the invention, the oxygenate impurity comprises dimethyl ether.
In another embodiment of this aspect of the invention, the product stream comprises at least about 1 mppm dimethyl ether, e.g., at least about 2.5 wt % dimethyl ether. As used herein and in the claims, the term xe2x80x9cmppmxe2x80x9d represents parts per million of a given component in a given stream on a molar basis.
In another embodiment of this aspect, the separating provides an oxygenate impurity-depleted stream which comprises no greater than about 100 mppm dimethyl ether, preferably no greater than about 50 mppm dimethyl ether, more preferably no greater than about 10 mppm dimethyl ether, say, no greater than about 1 mppm dimethyl ether.
In another embodiment of this aspect of the invention, the product stream comprises propylene.
In still another embodiment of this aspect of the invention, the separating is carried out by fractionating in a distillation column.
In yet another embodiment of this aspect of the invention, the converting is carried out without substantially converting said Cx olefin, i.e., no greater than about 5%, preferably no greater than about 2%, even more preferably no greater than about 0.1% of said Cx olefin is converted to non-Cx olefin compounds.
In still yet another embodiment of this aspect of the invention, the converting is carried out in the absence of added hydrogen.
In another embodiment of this aspect of the invention, the converting is carried out in the presence of added hydrogen.
In yet another embodiment of this aspect of the invention, the product stream comprises at least one member selected from the group consisting of methanol, water, CO and CO2, wherein said product stream is treated to remove at least some of said member, prior to said converting.
In still another embodiment of this aspect of the invention, the product stream containing said oxygenate impurity is derived from a process which converts oxygenates to olefins.
In yet another embodiment of this aspect of the invention, the boiling point differs by at least about 10xc2x0 C., preferably by at least about 25xc2x0 C., more preferably by at least about 50xc2x0 C.
In another aspect of this invention, the present invention relates to a process for at least partially removing from a product stream comprising Cx olefin wherein x is an integer ranging from 2 to 6, an oxygenate impurity selected from dimethyl ether, diethyl ether, di-n-propyl ether, diisopropyl ether, methylethyl ether, methyl-n-propyl ether, methylisopropyl ether, ethyl-n-propyl ether, ethylisopropyl ether, n-propylisopropyl ether, or mixtures thereof which comprises: converting said oxygenate impurity to a compound whose boiling point is at least about 5xc2x0 C. lower than said oxygenate impurity; and separating at least some of said compound from said Cx olefin.
In one embodiment of this aspect of the invention, the boiling point of said compound is at least about 5xc2x0 C., typically at least about 10xc2x0 C., say, at least about 25xc2x0 C., e.g., at least about 50xc2x0 C., lower than said oxygenate impurity and the converting step comprises contacting at least a portion of said product stream with a catalyst comprising a member selected from the group consisting of metal and metal compound. Typically, the catalyst comprises at least one member selected from the group consisting of group 3 (IIIA) metal, group 3 (IIIA) metal compound, group 4 (IVA) metal, group 4 (IVA) metal compound, group 5 (VA) metal, group 5 (VA) metal compound, group 6 (VIA) metal, group 6 (VIA) metal compound, group 7 (VIIA) metal, group 7 (VIIA) metal compound, group 8 (VIIIA) metal, group 8 (VIIIA) metal compound, group 9 (VIIIA) metal, group 9 (VIIIA) metal compound, group 10 (VIIIA) metal, group 10 (VIIIA) metal compound, group 11 (IB) metal, group 11 (IB) metal compound, group 12 (IIB) metal, and group 12 (IIB) metal compound.
In an embodiment of this aspect of the invention, the oxygenate impurity comprises dimethyl ether and said converting is carried out under conditions sufficient to convert said dimethyl ether to a mixture containing a member selected from the group consisting of methane, CO and CO2.
In another embodiment of this aspect of the invention, the catalyst comprises a member selected from the group consisting of group 11 (IB) metal and group 11 (IB) metal compound, e.g., Ag or a compound thereof, or copper or a compound thereof.
In yet another embodiment of this aspect of the invention, the catalyst comprises a group 11 (IB) metal or metal compound and an inorganic oxide, e.g., silver supported on alumina. Typically, the inorganic oxide support comprises at least one oxide selected from the group consisting of oxides of elements of groups 2-5, inclusive, Zn, groups 13, 14 (excluding carbon), and 15 (excluding nitrogen).
In still another embodiment of this aspect of the invention, the catalyst is a methanol synthesis catalyst, typically one which comprises copper, zinc oxide and alumina.
In still yet another embodiment of this aspect of the invention, no greater than about 1 wt %, say, no greater than about 0.1 wt % of said Cx olefin is converted by said converting step.
In another embodiment of this aspect of the invention, the conditions sufficient to convert said dimethyl ether comprise temperatures ranging from about 300xc2x0 to about 550xc2x0 C., and pressures ranging from about 60 to about 3500 kPaa.
In another aspect of this invention, the present invention relates to a process for at least partially removing from a product stream comprising Cx olefin wherein x is an integer ranging from 2 to 6, an oxygenate impurity selected from dimethyl ether, diethyl ether, di-n-propyl ether, diisopropyl ether, methylethyl ether, methyl-n-propyl ether, methylisopropyl ether, ethyl-n-propyl ether, ethylisopropyl ether, n-propylisopropyl ether, or mixtures thereof which comprises: converting said oxygenate impurity to a compound whose boiling point is at least about 5xc2x0 C., typically at least about 10xc2x0C., say, at least about 25xc2x0 C., e.g., at least about 50xc2x0 C., higher than said oxygenate impurity; and separating at least some of said compound from said Cx olefin. Typically, the converting comprises contacting at least a portion of said product stream with a supported metal catalyst comprising i) at least one member selected from the group consisting of group 8 (VIIIA) metal, group 8 (VIIIA) metal compound, group 9 (VIIIA) metal, group 9 (VIIIA) metal compound, group 10 (VIIIA) metal, group 10 (VIIIA) metal compound, group 11 (IB) metal, and group 11 (IB) metal compound, of the Periodic Table, and ii) a member selected from the group consisting of a porous inorganic oxide and microporous crystalline molecular sieve, said converting taking place at conditions sufficient to convert said oxygenate impurity to at least one higher boiling compound.
In one embodiment of this aspect of the invention, the converting is carried out in the absence of added hydrogen.
In an alternative embodiment of this aspect of the invention, the converting is carried out in the presence of added hydrogen.
In another embodiment of this aspect of the invention, the contacting is carried out in the presence of hydrogen and said supported metal catalyst is a hydrogenation catalyst.
In still another embodiment of this aspect of the invention, the contacting is carried out in the absence of hydrogen.
In another aspect, the present invention relates to a process for at least partially removing from a product stream comprising Cx olefin wherein x is an integer ranging from 2 to 6, an oxygenate impurity selected from dimethyl ether, diethyl ether, di-n-propyl ether, diisopropyl ether, methylethyl ether, methyl-n-propyl ether, methylisopropyl ether, ethyl-n-propyl ether, ethylisopropyl ether, n-propylisopropyl ether, or mixtures thereof which comprises: converting said oxygenate impurity to a compound whose boiling point is at least about 5xc2x0 C., typically at least about 10xc2x0 C., say, at least about 25xc2x0 C., e.g., at least about 50xc2x0 C., higher than said oxygenate impurity; and separating at least some of said compound from said Cx olefin. Typically, the converting comprises contacting at least a portion of said product stream with a supported metal catalyst comprising i) at least one member selected from the group consisting of group 8 (VIIIA) metal, group 8 (VIIIA) metal compound, group 9 (VIIIA) metal, group 9 (VIIIA) metal compound, group 10 (VIIIA) metal, group 10 (VIIIA) metal compound, group 11 (IB) metal, and group 11 (IB) metal compound, of the Periodic Table, and ii) a member selected from the group consisting of a porous inorganic oxide and microporous crystalline molecular sieve, said converting taking place at conditions sufficient to convert said oxygenate impurity to at least one higher boiling compound. The product stream comprises highly unsaturated C2 to C4 by-products comprising a member selected from the group consisting of an alkyne and an alkadiene. Optionally, additional amounts of a member selected from the group consisting of alkyne and alkadiene can be added as necessary, to react during said converting with unreacted oxygenate.
In one embodiment of this aspect of the invention, the alkyne comprises a member selected from the group consisting of acetylene, methyl acetylene, ethyl acetylene and dimethyl acetylene, and the alkadiene comprises a member selected from the group consisting of propadiene, 1,2-butadiene and 1,3-butadiene.
In another embodiment of this aspect of the invention, the C2 olefin fraction of the product stream or stream derived therefrom comprises at least 1 mppm of acetylene.
In still another embodiment of this aspect of the invention, the C3 olefins fraction of said product stream or stream derived therefrom comprises at least 1 mppm of methyl acetylene and/or at least 1 mppm of propadiene.
In yet another embodiment of this aspect of the invention, the C4 olefins fraction of the product stream or stream derived therefrom comprises at least 1 mppm of a member selected from the group consisting of ethyl acetylene, dimethyl acetylene, 1,2-butadiene and 1,3-butadiene.
In still yet another embodiment of this aspect of the invention, the converting provides at least partial hydrogenation of the member selected from the group consisting of alkyne and alkadiene by at least about 20%. The at least partial hydrogenation typically provides a member selected from the group consisting of ethylene, propylene and butene.
In yet another embodiment of this aspect of the invention, the oxygenate impurity comprises dimethyl ether. Typically, the C3 to C4 olefin fraction of said product stream or stream derived therefrom contains at least about 1 mppm oxygenates comprising dimethyl ether. The catalyst typically comprises at least one member selected from the group consisting of group 10 (VIII) and group 11 (1B) metals.
In another embodiment of this aspect of the invention, the catalyst comprises palladium.
In another embodiment of this aspect of the invention, the catalyst comprises silver.
In yet another embodiment of this aspect of the invention, the catalyst comprises palladium and silver.
In still another embodiment of this aspect of the invention, the catalyst comprises at least one of i) at least one porous inorganic oxide selected from the group consisting of silica, alumina, silica-alumina, zirconia, titania, aluminophosphate and clay, and ii) at least one microporous crystalline molecular sieve selected from the group consisting of silicates, aluminosilicates, substituted aluminosilicates, aluminophosphates, and substituted aluminophosphates. The catalyst optionally comprises iii) a member selected from the group consisting of a sulfur-containing moiety and oxygen-containing moiety.
In yet another embodiment of this aspect of the invention, the converting step is carried out in the liquid phase and comprises a temperature ranging from about 20xc2x0 C. to about 100xc2x0 C., total pressures ranging from about 1140 kPaa to about 4240 kPaa (from about 150 psig to about 600 psig), LHSV ranging from about 0.1 to about 100, and a hydrogen/(alkyne+alkadiene) ratio ranging from about 0.1 to about 100 on a molar basis.
In still another embodiment of this aspect of the invention, the converting conditions are carried out in the vapor phase and comprise a temperature ranging from about 20xc2x0 C. to about 600xc2x0 C., total pressures ranging from about 102 kPaa to about 4240 kPaa (from about 0.1 psig to about 600 psig), GHSV ranging from about 100 to about 20,000, and hydrogen partial pressure ranging from about 0.001 psig to about 200 psig.
In yet another embodiment of this aspect of the invention, the higher boiling compound is selected from at least one of acetone and methyl isopropyl ether.
In yet another embodiment of this aspect of the invention, at least 20%, typically at least about 50%, say, at least about 80%, of said dimethyl ether in the product stream is converted during the converting step.
Another aspect of the present invention relates to a process for at least partially removing dimethyl ether from a propylene-containing olefins stream which comprises converting at least a portion of said stream over a catalyst comprising metal and/or metal oxide, under conditions sufficient to selectively decompose said dimethyl ether to a mixture of methane, CO and CO2, in the presence of said olefins without substantially converting said olefins.
In one embodiment of this aspect of the invention, the catalyst comprises silver supported on alumina.
In another embodiment of this aspect of the invention, the catalyst comprises copper, zinc oxide and alumina.
In yet another embodiment of this aspect of the invention, the converting step is carried out in the absence of added hydrogen.
Another aspect of this invention relates to a process for at least partially removing oxygenate impurities from an olefin-containing stream produced by an oxygenate to olefin process which comprises: contacting an oxygenate feedstream with an olefin generation catalyst under conditions sufficient to provide a first product stream which contains C2 to C4 olefins, C2 to C4 paraffins, hydrogen, methane, oxygenates comprising dimethyl ether, and highly unsaturated C2 to C4 by-products comprising a member selected from the group consisting of an alkyne and an alkadiene; exposing at least a portion of the product stream or stream derived therefrom to a supported metal catalyst comprising i) at least one member selected from the group consisting of group 8 (VIIIA) metal, group 8 (VIIIA) metal compound, group 9 (VIIIA) metal, group 9 (VIIIA) metal compound, group 10 (VIIIA) metal, group 10 (VIIIA) metal compound, group 11 (IB) metal, and group 11 (IB) metal compound, of the Periodic Table, and ii) at least one of a porous inorganic oxide and microporous crystalline molecular sieve, said exposing taking place at conditions sufficient to convert said dimethyl ether to at least one higher boiling product; and removing at least some of said higher boiling product.
In an embodiment of this aspect of the invention, the exposing is carried out in the presence of hydrogen and said supported metal catalyst is a hydrogenation catalyst.
In another embodiment of this aspect of the invention, the exposing is carried out in the absence of hydrogen.
In still another embodiment of this aspect of the invention, the C3 to C4 olefin fraction of said product stream or stream derived therefrom contains at least 1 mppm oxygenates comprising dimethyl ether.
In yet another embodiment of this aspect of the invention, the alkyne comprises a member selected from the group consisting of acetylene, methyl acetylene, ethyl acetylene and dimethyl acetylene, and said alkadiene comprises a member selected from the group consisting of propadiene, 1,2-butadiene and 1,3-butadiene. The C2 olefin fraction of the product stream or stream derived therefrom typically comprises at least 1 mppm of acetylene, the C3 olefins fraction of the product stream or stream derived therefrom typically comprises at least 1 mppm of methyl acetylene and/or at least 1 mppm of propadiene, and the C4 olefins fraction of the product stream or stream derived therefrom comprises at least 1 mppm of a member selected from the group consisting of ethyl acetylene, dimethyl acetylene, 1,2-butadiene and 1,3-butadiene.
In still yet another embodiment of this aspect of the invention, the catalyst comprises a member selected from the group consisting of group 10 (VIII) and group 11 (IB) metals, e.g., palladium, or silver, or palladium and silver.
In another embodiment of this aspect of the invention, the catalyst comprises at least one of i) at least one porous inorganic oxide selected from the group consisting of silica, alumina, silica-alumina, zirconia, titania, aluminophosphate and clay, and ii) at least one microporous crystalline molecular sieve selected from the group consisting of silicates, aluminosilicates, substituted aluminosilicates, aluminophosphates, and substituted aluminophosphates. The catalyst can further comprise iii) a member selected from the group consisting of a sulfur-containing moiety and oxygen-containing moiety.
In still another embodiment of this aspect of the invention, the exposing conditions are carried out in the liquid phase and comprise a temperature ranging from about 20xc2x0 C. to about 100xc2x0 C., total pressures ranging from about 1140 kPaa to about 4240 kPaa (from about 150 psig to about 600 psig), LHSV ranging from about 0.1 to about 100, and a hydrogen/(alkyne+alkadiene) ratio ranging from about 0.1 to about 100 on a molar basis.
In yet another embodiment of this aspect of the invention, the exposing conditions are carried out in the vapor phase and comprise a temperature ranging from about 20xc2x0 C. to about 600xc2x0 C., total pressures ranging from about 102 kPaa to about 4240 kPaa (from about 0.1 psig to about 600 psig), GHSV ranging from about 100 to about 20,000, and hydrogen partial pressure ranging from about 0.001 psig to about 200 psig.
In still yet another embodiment of this aspect of the invention, the conversion of the dimethyl ether to at least one higher boiling product is at least about 20%, typically at least about 50%, say, at least about 80%.
In another embodiment of this aspect of the invention, the at least one higher boiling product is formed from the reaction of dimethyl ether with a member selected from the group consisting of the alkyne, the alkadiene and the propylene. Typically, the alkyne comprises methyl acetylene, the alkadiene comprises propadiene, and the higher boiling product is selected from a member selected from the group consisting of acetone and methylisopropyl ether. Additional amounts of a member selected from the group consisting of alkyne and alkadiene can be added as necessary, to react during the exposing with unreacted oxygenate.
In still another embodiment of this aspect of the invention, the exposing is carried out under conditions sufficient to effect at least partial hydrogenation of said member selected from the group consisting of alkyne and alkadiene at a conversion of at least about 20%, typically at least about 50%, say, at least about 80%.
In yet another embodiment of this aspect of the invention, the exposing is carried out under conditions sufficient to effect at least partial hydrogenation of said member selected from the group consisting of alkyne and alkadiene so as to provide a member selected from the group consisting of ethylene, propylene and butene.
In still yet another embodiment of this aspect of the invention, the removing of the higher boiling product is carried out by fractionating in a distillation column.
Another aspect of the invention relates to a process for at least partially removing oxygenate impurities from an olefin-containing stream produced by an oxygenate to olefin process which comprises: contacting an oxygenate feedstream with an olefin conversion catalyst under conditions sufficient to provide a first product stream which contains water, C5+ organic compounds, ethylene, propylene, butylenes and oxygenates comprising dimethyl ether, and unsaturated C2 to C4 by-products comprising a member selected from the group consisting of an alkyne and an alkadiene; at least partially removing said water, ethylene, butylenes and C5+ organic compounds from said first product stream to provide a second product stream enriched in propylene relative to said first product stream and comprising a member selected from the group consisting of an alkyne and an alkadiene, and containing dimethyl ether; exposing at least a portion of said second product stream in the presence of hydrogen to a hydrogenation catalyst comprising i) at least one member selected from the group consisting of group 8 (VIIIA) metal, group 8 (VIIIA) metal compound, group 9 (VIIIA) metal, group 9 (VIIIA) metal compound, group 10 (VIIIA) metal, group 10 (VIIIA) metal compound, group 11 (IB) metal, and group 11 (IB) metal compound, of the Periodic Table, and ii) a member selected from the group consisting of a porous inorganic oxide and microporous crystalline molecular sieve, said exposing taking place at conditions sufficient to simultaneously effect 1) conversion of said dimethyl ether to at least one higher boiling product, and 2) at least partial hydrogenation of said member selected from the group consisting of alkyne and alkadiene; thereby providing a third product stream; and removing said higher boiling product from said third product stream.
In another aspect of the invention, the present invention relates to a process for at least partially removing from a product stream comprising Cx olefin wherein x is an integer ranging from 2 to 6, an oxygenate impurity selected from dimethyl ether, diethyl ether, di-n-propyl ether, diisopropyl ether, methylethyl ether, methyl-n-propyl ether, methylisopropyl ether, ethyl-n-propyl ether, ethylisopropyl ether, n-propylisopropyl ether, or mixtures thereof which comprises: converting said oxygenate impurity to a compound whose boiling point differs by at least about 5xc2x0 C. from said oxygenate impurity; and separating at least some of said compound from said Cx olefin. Typically, the converting step is carried out in the presence of H2O with an acid catalyst under conditions sufficient to at least partially convert said oxygenate impurity to its corresponding alcohol(s).
In one embodiment of this aspect of the invention, the oxygenate impurity is dimethyl ether and the corresponding alcohol is methanol.
In another embodiment of this aspect of the invention, the product stream comprises propane. The propane-containing stream is typically derived from an oxygenate to olefins conversion process effluent.
In still another embodiment of this aspect of the invention, the catalyst is a non-shape selective acid catalyst, e.g., gamma-alumina.
In yet another embodiment of this aspect of the invention, the conditions comprise a temperature ranging from about 300xc2x0 C. to about 800xc2x0 C. and a weight ratio of the dimethyl ether to the H2O of no greater than about 2.5, typically, a temperature of at least about 500xc2x0 C. and a weight ratio of the dimethyl ether to the H2O ranging from about 1.2 to about 2.5, say, a temperature ranging from about 600xc2x0 C. to about 800xc2x0 C. and a weight ratio of the dimethyl ether to the H2O ranging from about 0.5 to about 2.5.
In still yet another embodiment of this aspect of the invention, the conditions provide at least about 25% to about 95% conversion of the dimethyl ether to methanol, typically at least about 90% conversion of the dimethyl ether to methanol, say, at least about 92% conversion of said dimethyl ether to methanol.
In another embodiment of this aspect of the invention, at least some of the H2O is steam.
In still another embodiment of this aspect of the invention, at least some of the H2O is separated along with said methanol in the separation step.